/*
2021-8-17
https://www.acwing.com/problem/content/304/
*/
#include<cstring>
#include<iostream>
#include<algorithm>

using namespace std;
typedef long long ll;
const int N=3e5+5;
ll t[N],c[N];
ll f[N];
int q[N];
int n,s;

int main()
{
    ios::sync_with_stdio(false);
    cout.tie(NULL);
    
    cin>>n>>s;
    for(int i=1;i<=n;i++)
    {
        cin>>t[i]>>c[i];
        t[i]+=t[i-1];
        c[i]+=c[i-1];
    }
    
    int hh=0,tt=0;
    q[0]=0;
    
    for(int i=1;i<=n;i++)
    {
        int l=hh,r=tt;
        while(l<r)
        {
            int mid=l+r>>1;
            if(f[q[mid+1]]-f[q[mid]]>(t[i]+s)*(c[q[mid+1]]-c[q[mid]])) r=mid;
            else l=mid+1;
        }
        int j=q[r];
        f[i]=f[j]-(t[i]+s)*c[j]+t[i]*c[i]+s*c[n];
        while(hh<tt && (double)(f[q[tt]]-f[q[tt-1]])*(c[i]-c[q[tt-1]])>=(double)(f[i]-f[q[tt-1]])*(c[q[tt]]-c[q[tt-1]])) tt--;
        q[++tt]=i;
    }
    cout<<f[n]<<endl;
    return 0;
}
